Electronic devices



July 14, 1959 o. E. H. RYDBECK 7 ELECTRONIC DEVICES Filed March 13, 1956ATTORNEYS,

United States atent ELECTRONIC DEVICES Olof Erik Hans Rydbeck, Goteborg,Sweden Application March 13, 1956, Serial No. 571,277 Claims priority,application Sweden March 18, 1955 8 Claims. c1. 315-5.15)

The present invention relates to an electronic device with at least twocooperating electron beams. The problem to be solved by the inventionwas to investigate whether and-under what conditions a cooperation cantake place between two intersecting electron beams, i.e. a cooperationthat can be used in practice, particularly in such cases where the useof known arrangements is limited. Thus, the object of the invention isto provide an electronic device in which these conditions are fulfilledor may be fulfilled in a simple manner.

An electronic device according to the invention is characterized bymeans for generating a first electron beam, means for generating asecond electron beam, a space, preferably of wave-guide character, inwhich the beams are caused to intersect each other, and means forimposing upon the first and/ or the second beam such electron velocityor other character that a desired cooperation between the beams, e.g.for amplification, attenuation, generation of oscillations etc., isobtained.

A device according to the invention may be carried out in different waysand two types will be described hereinafter having different operationsin certain respects, with reference to the accompanying drawings. Thedrawing figures illustrate schematically the structural features of theembodiments.

Fig. 1 shows one embodiment of a device according to the invention.

Fig. 2 is a sectional view of a wave guide incorporated in the deviceaccording to Fig. '1. Fig. 3 is a sectional view of an alternative formof wave guide to that shown in Fig. 2.

Fig. 4 shows another embodiment of the invention.

Fig. 5 shows still another embodiment of the invention.

Figs. 6 and 7 show alternative embodiments of the wave guides of thedevice.

In the first type of the device according to the invention a velocitymodulation is imposed upon one of the two electron beams, whichhereinafter is denoted as the first electron beam, said modulation beingobtained, for instance, by means of a modulation helix or a cavityresonator, whereafter the beam is caused to pass through said spacehaving wave guide character, where it is in tersected perpendicularly bythe second electron beam, which is homogeneous and in which the electronvelocity is adjusted to a suitable value.

The other type of the device according to the invention differs from theabove-mentioned first type in that the second electron beam is nothomogeneous, i.e. has not a constant electron density, seen in thedirection of the first electron beam, but has a periodically varyingelectron density.

In both said types amplification of the oscillations imposed bymodulation of the first electron beam may be obtained under certainconditions which will be more definitely stated in the following.

In the device according to Fig. 1 which belongs to the first type, afirst electron beam I is generated by an electron gun 3 together withelectron optical means for pro- 2,895,072 Patented July 14, 1959 ducinga homogeneous beam of parallel electron rays passing in the axialdirection through a wave guide 1 to a collector 5. The beam I ismodulated in velocity when passing through a resonator system 7 of anyconventional construction having an input 9 for a coupling lead. Aresonator system 11 at the end of the wave guide through which systemthe electron beam passes serves as an output resonator from which theoscillations may be taken which are obtained from the electron beam Iafter its passage through the wave guide. The hatched parts of thedrawing figures designate insulating material (glass).

In the shown embodiment the wave guide 1 has rectangular cross sectionas shown in Fig. 2 which corresponds to the sectional line AA in Fig. 1,said cross section being substantially wholly occupied by the electronbeam I. This beam has previously been formed to a corresponding shape bythe electron optical means referred to in connection with the electrongun. The one longitudinal side 15 of the wave guide is provided with agreat number of apertures through which the electrons of the secondelectron beam H which is perpendicular to the first electron beam 1 andis designated as the cross beam in the following description may passinto the wave guide. The apertures in the wall 15 are so small that thecharacter of the device 1 as a wave guide for the high frequencyoscillations of the electron beam I is not lost. The side wall 15 mayeither be galvanically connected to the rest of the wave guide or may begalvanically but not for high frequencies insulated from the rest of thewave guide as will be described in more detail hereinafter.

The cross beam II is generated by a cathode 17 extending parallel to thewall 15 at a suitable distance therefrom. The acceleration voltage forthe electrons of the cross beam may be applied between the cathode 15and the wave guide 1, and furthermore one or more control grids 19 maybe arranged between the cathode 17 and the wall 15 as in the shownembodiment.

It has now been found that in the embodiment shown in Fig. 1 anamplification of the oscillations modulated upon the electron beam I isobtained owing to cooperation between the beam I and the cross beam II,if the velocity v of the electrons of the cross beam is adjustedapproximately to a such value that c =the velocity of light 7 a=thecross dimension of the wave guide in the direction of the cross beam x=the wave length in vacuum of the oscillations n=an integer l, 2, 3 etc.

The acceleration voltage V which is required for accelerating theelectrons of the cross beam to the velocity v may suitably be adjustablein a manner known per se and, furthermore, it is possible to adjust thevelocity of the electrons in the shown embodiment by varying thepotential of the control grid 19.

The mechanism of the process resulting in an amplification of theoscillations of the electron beam I is difficult to illustrate inanother way than by a relatively complicated mathematical treatmentwhich, applied to a device having a wave guide with rectangular crosssection, gives as result the conditions stated above. Thus, thiscondition is true substantially only in such cases where the crosssection of the wave guide is rectangular and, besides, under the otherconditions mentioned above.

In order that the velocity v of the electrons of the cross beam may beconstant and equal substantially everywhere in the wave guide whichcondition is difficult to fulfill in a Wave guide in which the wallprovided with the apertures is galvanically connected to the rest of thewave guide owing to space charge effects tending to deflect and retardthe electrons in the wave guide, it may be suitable to insulate thewall- 15 from the rest of-the wave guide with respect to direct currentfor instance in the manner shown in Fig. 3, where the wall 15 isconnected to or provided with flanges 21 which together with the waveguide body and an interposed insulating dielectric 23 form a capacitanceserving substantially as a short circuit for the high frequency currentsin the wave carrier mantle, a suitable voltage difierence being appliedbetween the wall 15 and the wave carrier body 1 for maintaining adesired velocity and directionof the electrons of the cross beam at aconstant value, which is desired in order that the above mentionedcondition shall be fulfilled substantially everywhere in the1wave guide.

It can be shown that the band width ZAw/w of the amplification, where cais the angular frequency in vacuum of the oscillations modulated uponthe primary electron beam I roughly corresponds to the expression wherew i is the plasma angle frequency of the cross beam.

p In the following example it has been supposed that the vacuum wavelength'k is 20 cm. When in the expressionfor the amplification above Itis chosen to be equal to l (the lowest mode of oscillations) one arriveswith a=1 to the expression v /c =0.1. Since where V is the accelerationvoltage for the cross beam, and e and m are the charge and the massrespectively of the electron, the condition for amplification will befulfilled at a value of V of the order of 2500 v.

As an example as to the band width it is assumed that the vacuum wavelength is 20 cm. as above, while the current density of the cross beamis approximately 0.5 Ina/mm. and the acceleration voltage for the crossbeam is approximately 1000 v. In this case a band width maybe obtainedwhich is roughly equal to /21r, which can be considered as a very highvalue and is sulficient in most connections.

In the described embodiment it was assumed that only the electron beam Iwas subjected to modulation (velocity modulation). However, it ispossible to modulate also the cross beam II with another frequency, inwhich case a frequency mixing operation may be obtained, the resultingsignals being taken from the resonator 11 according to the drawing.

If the frequency modulated upon the cross beam is considerably lowerthan the high frequency modulated upon the electron beam I the higherfrequency may be modulated by the lower frequency by interaction betweenthe two beams in the wave guide, the modulated. high frequency beingtaken from the resonator 11. as-in the case justmentioned.

In analogy with the conditions in conventional amplifier tubes it is, ofcourse, possible to use feedback in the device according to theinvention, it being possible to bring thedevice into self-oscillations(as an oscillator.) by coupling the resonators 7 and 11 'to each otherin a suflicient degree in a manner known per se.

The condition. for obtaining amplification as stated above isfundamentally independent of the intensity, i.e. the current density ofthe cross beam, A variation of this current density will thus not changematerially the COH dItIOIIS for obtaining amplification but it willhavean Influence upon the resulting band width in such manner, that the bandwidth is substantially proportional to the square root of the currentdensity.

In the drawings no means for supplying electrode poten 4, tials, forcathode heating etc., are shown, since these means may be of anyconventional construction.

Fig. 4 shows schematically a device of the other type of the inventionin longitudinal section. The figure shows only the wave guide 1 with thewall 15 which is permeable to electrons and further the means for thegeneration of the cross beam II, it being assumed that the device inother respects corresponds to the one shown in Fig. 1. In the deviceshown in Fig. 4 the first electron beam I is homogeneous and subjectedto velocity modulation as in the type described above. However, thecross beam II is not homogeneous but has an electron density whichvaries in the direction of the electron beam 1, as is illustrated by thecurve 33 in Fig. 4, the'variation being periodic with the structure wavelength A,,. This variation may be obtained in different ways forinstance by using a control grid 31 with periodically varying pitch orDurchgritf (shielding factor) as according to Fig. 4, but the variationmay also be obtained in other ways, for instance by using a cathode 17having periodically varying electron emission ability. I

It has been found that in such a device it is possible to obtainamplification of the oscillations modulated upon the electron beam I byinteraction between the electron beam I and the cross beam II in thewave guide 1, said amplification being independent. of the electronvelocity of the cross beam if where h is the plasma wave length of theelectron beam I, said condition being true for the embodiment shownschematically in Fig. 4. In other words this expression means that inFig. 4 ba=A,,/4, where w and b are the distances from the input end ofthe wave guide 1 to the adjacent and maximum respectively of the maincomponent (fundamental) of the cross beam II. For optimalamplificationthe distance a should be chosen so that a1=?\,,/ 8. If b= /8, which maybe fulfilled for instance by shaping the control grid 31 or the cathodein a suitable manner, a weakening or attenuation of the oscillations isobtained instead of amplification. However, in certain cases also suchweakening may be useful in practice. 7

If A, does not satisfy the condition statedabove an amplification may beobtained only if the electron velocity in the cross-beam is adjusted toa suitable value. Such adjustment may be effected in the, mannersdescribed in connection with Fig. 1. 5

Further, it should be pointed out that it is not necessary that thevariations of the electron density of cross beam II in the direction ofthe electron beam I strictly follow a sine curve, since the Wave form ofthe variation may be of other shape, as is indicated in Fig. 4 by meansof a dashed curve, it being. suflicient that the variation has acomponent (especially a fundamental) the wave length of which fulfillsthe above condition in order that the electron velocity of the crossbeam shall not be criticalwith respect to the amplification. Thus, itmay be possible to obtain the variation of the current density byarranging instead of the control grid 31 a number of screens or the likein a regular mutual distance 7\,=A,,/ 2 in the direction of the electronbeam Ior by using a plurality of shorter cathodes 17 distributedregularly in the same manner along the electron beam I. As analternativealso the wall 15 may be shaped in such manner that it can pass electronsonly in certain zones regularly dis tributed in the mariner described.

Also this type of the device according to the invention offers thepreviouslystatedpossibilities as to feedback and modulation of the crossbeam (for frequency mixing and modulation of the .primary beam 1).

According to the invention itiis possible by modifying the electricconductance, of the conducting inner surface of the waveguide to changethe band width of the amplification-obtained. Thus, itzwould be possibleto increase 5 this band width, though on the cost of the maximumamplification, in this band by applying graphite on the inner surface ofthe wave guide or by treating this surface in another way for reducingits conductance.

The amplification obtained in a device according to the invention isdependent upon the length 1 of the wave guide, i.e. its dimension in thedirection of the primary beam I, so that the total amplification may becalculated as the amplification per unit length of the Wave guidemultiplied with the length of the wave guide. It is not necessary thatthe amplification per unit length is constant along the wave guide. Thusit is possible by arranging several electrode systems or electrodes, forinstance several control grids or cathodes, for the generation ofseveral cross beams, to obtain an amplification which depends upon asmany factors as the number of different electrode systems and electrodesrespectively for cross beams, so that the amplification may beinfluenced by several different signals each applied to one of saidelectrode systems or electrodes. Such a device may be suitable forinstance for modulation (or impulsation) of a carrier frequency byseveral independent signals. Fig. 5 shows schematically a device of thiskind, only the wave guide of the tube and the means for generating crossbeams being shown in longitudinal section as in Fig. 4. Fig. 5 showsfour electrode systems A, B, C and D having cathodes 35 and grids 37 forthe generation of the cross beams H I1 I1 and II but fewer or moresystems may of course be used. Each electrode system A-D will evidentlycooperate with and efiect the primary beam I independently of the otherelectrode systems, so that the output signal obtained from the beam IWill contain components derived from the difierent signals applied tothe systems A-D. These systems may fundamentally be of any desired type,for instance either of the type shown in Fig. l or of the type shown inFig. 4 or of bothtypes.

The arrangement shown in Fig. 5 for influencing a primary beam I bymeans of different signals may of course be modified in different wayswithout fundamentally changing its function. Thus, it is possible toarrange instead of several cathodes or grids either a single longcathode and several control grids or several cathodes and a singlecontrol grid. Further it is not necessary that the electrode systems A-Dare arranged side by side, but the cross beams may be directed into theprimary beam I from different directions. and, if desired, in a singlearea, which may be suitable in certain cases, for instance in view ofstructural facilities.

The embodiments shown in Figs. 1-5 are provided with a space in the formof a wave guide 1, in which the electron beams I and II cooperate. Thedesired cooperation, however, is not necessarily limited to the use of aspace of this character, since a cooperation is always obtained in thearea in which the beams intersect each other under the previously statedconditions relating to the circumstances in a device having twoperpendicular electron beams. In this connection it is important topoint out that it is not necessary that the two beams are exactlyperpendicular, since, fundamentally, a cooperation occurs even if thecross beam has only a velocity component perpendicular to the primarybeam. Since the mutual cooperation between two parallel and mutuallycoupled electron beams is previously known, there may be, in a deviceaccording to the invention with beams obliquely intersecting each other,a question of superposition of two effects arising from the cooperationbetween the primary beam and the component parallel therewith and thecomponent perpendicular thereto respectively of the cross beam.

Though the wave guide 1 in the embodiments shown in Figs. 1-5 wereassumed to be rectangular in cross section, it may be preferred to useanother form of Wave guide. The condition for obtaining the desiredcooperation between the electron beams mentioned in connection with Fig.1 may then have another form than that stated above. In such cases whereit is diflicult to calculate theoretically said condition there remainsalwaysas stated above--'the possibility of obtaining the conditions forthe desired cooperation by varying the potentials of the electrodesystems of the two electron beams. Figs. 6 and 7 show examples of twoalternative embodiments with circular wave guides and a correspondingform of the electrode system for the cross beam.

According to Fig. 6 the wave guide consists of two coaxial cylindricwalls 41 and 43 the inner wall 43 being permeable to electrons in thesame manner as the Wall 15 in Figs. 1 and 5. In the zone-formed space inthe wave guide an axial electron beam passes which constitutes theprimary beam I. A cross beam II is generated by the cathode 45 in thecenter of the wall43, a control grid 47 being provided around thecathode for controlling the electron velocity of the cross beam formodulation or impulsation of same.

In the device according to Fig. 7 the wave guide consists of an innercylindrical wall 51 and an outer wall 53 coaxial therewith and havingperforations, the primary beam I passing axially between said walls.From an outer, cylindrical cathode 55 a cross beam II passes through thewall 53 into the wave guide 51, 53 in which the desired cooperationbetween the beams takes place. Also in this arrangement one or morecontrol grids 57 may be arranged between the cathode 55 and the wall53which is permeable to electrons.

The invention is not limited to the embodiments described and shown,since these embodiments may be modified in the abovementioned respectsand also in other respects within the scope of the invention.

What I claim is:

1. An electronic device comprising a wave guide having a space therein,a first source of charged particles positioned to direct a stream ofsaid particles axially along said wave guide space, a second source ofcharged particles positioned to direct a second stream of chargedparticles substantially at right angles to said first stream ofparticles along a substantial portion of said wave guide, and means forvarying said second stream of changed particles to modulate said firststream of charged particles, said second electron beam having a velocitycomponent v which approximately fulfills the condition c =the velocityof light a=the cross dimension of the wave guide in the direction of thecross beam x =the wave length in vacuum of the oscillations n=aninteger.

2. An electronic device comprising a hollow wave guide having a circularcross section, a first source of charged particles positioned to directa stream of said particles axially along said wave guide, a secondsource of charged particles positioned to direct a second stream ofcharged particles substantially at right angles to said first stream ofparticles along a substantial portion of said wave guide, and means forvarying said second stream of charged particles to modulate said firststream of charged particles comprising a second cylindrical memberconcentrically arranged within said wave guide intermediate said secondsource of charged particles and said stream of charged particlesproduced by said first source, the walls of said second cylindricalmember being permeable to the particles of said second source.

3. An electronic device comprising a hollow wave guide, a first sourceof charged particles positioned to direct a stream of said particlesaxially along said wave guide, a second source of charged particlespositioned to direct a second stream of charged particles substantiallyat right angles to said first stream of particles along a substantialportion of said wave guide, and means for varying the current density ofsaid second stream of charged particles to modulate said first stream ofcharged par ticles comprising a control grid positioned intermediatesaid second source and said first stream of particles, and means forperiodically varying the shielding factor of said control grid.

4. An electronic device comprising a hollow wave guide, a first sourceof charged particles positioned to direct a stream of said particlesaxially along said wave guide, a second source of charged particlespositioned to direct a second stream of charged particles substantiallyat right angles to said first stream of particles along a substantialportion of said wave guide, and means for varying the current density ofsaid secondstream of charged'particles to modulate said first stream ofcharged particles, comprising means for periodically varying theemission ability of said second source.

5. An electronic device comprising a hollow wave guide, a first sourceof charged particles positioned to direct a stream of said particlesaxially along said wave guide, a second source of charged particlespositioned to direct a second stream ofcharged particles substantiallyat right angles to said first stream of particles along a substantialportion of said wave guide, and means for varying the current density ofsaid second stream of charged particles to modulate said first stream ofcharged particles, the wave length of the variation of the currentdensity of said second stream of changed particles as seen in thedirection of the first stream of charged particles being approximatelyequal to half the plasma wave length of the first stream of chargedparticles.

6. An electronic device as defined in claim wherein the distance betweenthe input end of said wave guide and the nearest minimum or maximum peakof the main component of the variation of the current density of thesecond stream of charged particles is equal to A3 of the plasma wavelength of the first stream of charged particles.

7. An electronic device comprising a hollow wave guide, a first sourceof charged particles positioned to direct a stream of said particlesaxially along said wave guide, a plurality of auxiliary sources ofcharged particles arranged to directsecond streams of saidparticles atright angles to said first stream of particles, and means for applyingcontrol signals to each of said auxiliary sources to periodically varythe current densities of said second particle streams and thus modulatesaid first stream of particles.

8. An electronic apparatus comprising a wave guide having a rectangularcross-section, an-electron gun positioned to direct a first stream ofelectrons axially within said wave guide, one longitudinal side of saidwave guide being permeable to electrons, a cathode parallel to andspaced from said permeable longitudinal wave guide side, said cathodeextending substantially the length of said permeable wave guide side,circuit means causing said cathode to produce a second stream ofelectrons through said permeable wave guide side at right angles to saidfirst stream of electrons substantially along the length of said waveguide, and means for periodically varying the density of said secondstream of electrons to modulate said first stream of electronscomprising a control grid intermediate said cathode and said permeablelongitudinal wave guide side, said control grid having a lengthsubstantially equal to the length of said cathode, the periodicvariation of current density of said second stream of electrons beingeifected by a periodic variation of the effective shielding factor ofsaid control grid.

References Cited in the file of this patent UNITED STATES PATENTS2,229,752 Jonker et a1. Jan. 28, 1941 2,607,861 Wagner Aug. 19, 19522,684,453 Hansell July-20, 1954 2,694,159 Pierce Nov. 9, 1954 2,730,647Pierce Ian. 10, 1956

